Transmission control

ABSTRACT

An automatic transmission control having a transition valve controlled by a transmission gearing member to maintain one transmission drive engaged to drive a load until another transmission drive is established with sufficient torque capacity to drive the load.

United States Patent [72] Inventor Robert E. Annis Howell, Mich.

[2]] Appl. No. 64,978

[22] Filed Aug. 19, 1970 [45] Patented Jan. 11, 1972 [73] AssigneeGeneral Motors Corporation Detroit, Mich.

[54] TRANSMISSION CONTROL 3 Claims, 2 Drawing Figs.

[52] US. Cl 74/751, 74/731, 74/869 [51] Int. Cl ..Fl6h 47/00, Fl6h 3/74,l 360k 2 1/10 COOLER v 5 MODULATOR VALVE [5 0] Field of Search 74/869,751, 731

' [56] References Cited UNITED STATES PATENTS 2,946,241 7/1960 Synder74/751 X 3,303,726 2/1967 Christensen 74/75l Primary ExaminerArthur T.McKeon Attorneys-W. E. Finken, A. M. Heiter and R. L. Phillips ABSTRACT:An automatic transmission control having a transition valve controlledby a transmission gearing member to maintain one transmission driveengaged to drive a load until another transmission drive is establishedwith sufficient torque capacity to drive the load.

l-2 TRANSITION VALVE PATENTEU m1 1 1972 3633.439

SE RVO COOLER $4 46 MODULATOR VA LVE INVEJ TOR BY waif/52%; 2% Z [WWWATTORNET TRANSMISSION CONTROL This invention relates to transmissionsand more particularly to transmission controls for providing shiftingwithout drive interruption.

The transmission control according to the present invention has atransition valve that controls an exhaust of a shift valve to time thedisengagement of one drive with the engagement of another drive. In thetransmissions gearing arrangement there is a member which undergoes loadreversal during shifting between these drives and this member is used tocontrol the transition valve so that the fluid pressure effectingestablishment of the one transmission drive is maintained on a shiftuntil the other transmission drive is established with sufficient torquecapacity to drive the load.

An object of the present invention is to provide a new and improvedtransmission control.

Another object is to provide -a transmission control that maintains onetransmission drive until another transmission drive is established withsufficient torque capacity to drive a load by control of a transmissiongearing member which undergoes load reversal during such shifting.

Another object is to provide in a transmission control for atransmission including gearing having a member which undergoes loadreversal during shifting, a transition valve that cooperates with ashift valve to maintain a fluid pressure bias effecting establishment ofthe one transmission drive to drive a load only until anothertransmission drive is established with sufficient torque capacity todrive the load.

These and other objects of the invention will be more apparent from thefollowing description and drawing in which:

FIG. 1 is a schematic view of a transmission drive train and controlsystem therefor according to the present invention.

FIG. 2 is a partial sectional view of an actual construction of part ofthe transmission drive train and control system shown schematically inFIG. 1.

TRANSMISSION DRIVE TRAIN ARRANGEMENT The control system according to thepresent invention is particularly suited for controlling vehicletransmissions of the type shown in FIG. 1. The transmissions drive trainarrangement generally comprises a hydrodynamic torque converter 10,planetary gear sets 12 and 14 and a plurality of fluid pressure operateddrive establishing devices all housed in a transmission housing 15. Thetransmission is operable to provide four forward drives, neutral and areverse drive. The forward drives are provided by two gear reductiondrives, a direct drive and a geared overdrive.

Describing now the train arrangements details beginning at the frontend, the hydrodynamic torque converter is of a conventionalthree-element type having a pump 16, a turbine 18, and a stator 19 whichis groundable to the transmission housing by a one-way brake 20. Thepump 16 is adapted to be driven by the vehicles engine and the turbine18 is connected to a converter output shaft 21. When the engine isoperating to power converter 10, the converter operates to drive theconverter output shaft 21 in what will be described as the forwarddirection by providing torque multiplication from stall up to couplingspeed and fluid coupling operation thereafter.

Converter output shaft 21 which serves as the input shaft to theplanetary gearing, is connected at its rear end to a drum 24 in which islocated two clutches 26 and 28 and a brake 29. The clutch 28 comprises afriction plate pack in which alternate plates are splined to drum 24 andthe remaining plates are splined to a hub 31 that is connected to thefront end of a sleeve shaft 32. A piston 34 mounted in a cylinder indrum 24 is urged on delivery of fluid under pressure to a chamber 35, toengage the plates of clutch 28 and thus connect the converter outputshaft 21 to shaft 32. Suitable retraction springs, not shown, biaspiston 34 towards its clutch release position.

The brake 29 comprises a friction plate pack in which alternate platesare splined to hub 31 and the remaining plates are splined to a bulkhead36that is rigidly secured to transmission housing 15. A piston 38mounted in a cylinder in bulkhead 36 is urged on delivery of fluid underpressure to a chamber 39 to engage the plates of brake 29 and thus brakethe shaft 32. Suitable retraction springs, not shown, bias the piston 38towards its brake release position.

The clutch 26 comprises a friction plate pack in which alternate platesare splined to drum 24 and the remaining plates are splined to a hub 41that is connected to the front end of a shaft 42 which extends throughsleeve shaft 32. A piston 44 mounted in a cylinder in drum 24 is urgedon delivery of fluid under pressure to a chamber 46 to engage the platesof clutch 26 and thus connect the converter output shaft 21 to shaft 42.Suitable retraction springs, not shown, bias the piston 44 towards itsclutch release position.

In the planetary gearing, the gear set 14 is located at the rear of thetransmission behind the other gear set 12. Both gear sets 12 and 14 areof the simple helical planetary gear type. The front gear set 12comprises an annular sun gear 50, a ring gear 51 and a planet carrier 52carrying a planet pinion 54 in mesh with sun gear 50 and ring gear 51.The sun gear 50 is connected to the rear end of sleeve shaft 32 and thecarrier 52 is connected to the rear end of shaft 42. The rear gear set14 comprises an annular sun gear 56, a ring gear 58 and a planet carrier59 carrying a planet pinion 61 in mesh with sun gear 56 and ring gear58. The ring gear 58 is connected to a drum 62 which is also connectedto carrier 52 of the front gear set 12. Both the carrier 59 of rear gearset 14 and ring gear 51 of front gear set 12 are connected to a hub 64.Hub 64 is connected to the front end of a shaft 66 which is suitablysupported in the rear end of the transmission housing 15 and serves asthe transmission s output.

A brake 68 and a one-way brake 69 are connected in series forselectively holding sun gear 56 of rear gear set 14 against backwardrotation. The brake 68 comprises a friction plate pack in whichalternate plates are splined to transmission housing 15 and theremaining plates are splined to the outer race 70 of one-way brake 69. Apiston 71 mounted in a cylinder in transmission housing 15 is urged ondelivery of fluid under pressure to a chamber 72 to engage the plates ofbrake 68 and thus brake the outer race 70. Suitable retraction springs,not shown, bias piston 71 towards its brake release position. Theone-way brake 69 which may be of any suitable conventional type has itsinner race 76 connected to sun gear 56 of rear gear set 14 by a sleeveshaft 77 through which output shaft 66 extends. The directional sense ofthe one-way brake 69 is such that when brake 68 is engaged, the one-waybrake 69 is then operable to prevent reverse rotation of sun gear 56while permitting free forward rotation thereof.

In addition to the selective prevention of reverse rotation of sun gear56, there is provided a brake 78 which prevents any rotation thereof.The brake 78 comprises a friction plate pack in which alternate platesare splined to transmission housing 15 and the remaining plates aresplined to a hub 79. Hub 79 is connected to the rear end of shaft 77 andis thus connected to sun gear 56. A piston 81 mounted in a cylinder intransmission housing 15 is urged on delivery of fluid under pressure toa chamber 82 to engage the plates of brake 78 and thus brake sun gear56. Suitable retraction springs, not shown, bias piston 81 towards itsbrake release position.

A friction band brake 86 is grounded to transmission housing 15 and isoperated by a servo 87 of any suitable conventional type. The brake 86is urged on delivery of fluid under pressure to servo 87 to engage drum62 and thus brake carrier 52 of front gear set 12.

Describing now the operation made available by the drive trainarrangement described above, neutral is established by engaging clutch28 while all the other fluid pressure operated clutches and brakes arereleased. The engagement of clutch 28 readies the transmission forestablishment of either forward or reverse drive as will become moreapparent later, but no power from the converter output shaft 21 can betransmitted through the gearing to the transmission output shaft 66.

The first and lowest speed range forward drive is established bymaintaining engagement of clutch 28 and engaging brake 68. Power fromthe forwardly rotating converter output shaft 21 is delivered throughthe engaged clutch 28 to drive sun gear 50 in front gear set 12forwardly. The other sun gear 56 tries to rotate backwardly but isprevented from doing so by the one-way brake 69 since brake 68 isengaged. The planetary gearing, then, by compound action drives thetransmission output shaft 66 in the forward direction and at a reducedspeed relative to converter output shaft 21. In the first forward drivethus established, power cannot be transmitted from the output shaft tothe converter for engine braking because of the one-way brake 69 andthus the transmission output shaft 66 can overrun when the vehicle iscoasting. In the first forward drive, the brake 78 may be engaged toprevent forward rotation of sun gear 56 to provide for reverse powertransmittal and thus provide for engine braking.

The second and next higher speed range forward drive is established bymaintaining engagement of brake 68, releasing clutch 28 and engagingclutch 26. Input power is now delivered through the engage clutch 26 todrive ring gear 58 of rear gear set 14 forwardly. The sun gear 56 triesto rotate backwardly but again is prevented from doing so by the onewaybrake 69 since brake 68 is still engaged. Planet pinion 61 thereforewalks forwardly around sun gear 56 and drives carrier 59 and connectedoutput shaft 66 forwardly at a reduced speed but in a speed range higherthan that of the first forward drive. In the second forward drive, thebrake 78 may be engaged like in the first forward drive to provide forengine braking during vehicle coasting.

For the purpose of fully understanding the transmission controlaccording to the present invention, it is necessary to know that theinput driven helical sun gear 50 of the front gear set 12 is forcedrearwardly or to the right by the thrust of the helix in the firstforward drive and on a shift to the second forward drive, the helixforces sun gear 50 frontwardly or to the left. This load reversal of thesun gear 50 which is a member of the planetary gearing is used to timethe disengagement of the first forward drive with the engagement of thesecond forward drive as described in more detail later.

The third and next higher speed range forward drive is established bymaintaining engagement of brake 68 and clutch 26 and additionallyengaging clutch 28. With clutches 26 and 28 engaged, the carrier 52 andthe sun gear 50 in front gear set 12 are connected and are thus bothdriven in the forward direction at converter output speed. Thus, thefront gear set 12 is effectively locked up and provides a 1:1 speedratio or direct drive between the converter output shaft 21 andtransmission output shaft 66. In the third forward drive, the rear gearset 14 is also locked up by its connections with the front gear set 12and therefore the sun gear 56 in this gear set also rotates in theforward direction at converter output speed. Thus the brake 68 mayremain engaged on the shift to the third forward drive since the one-waybrake 69 permits forward rotation of sun gear 56. With the gearing thuslocked up, engine braking is made available in this drive.

The fourth and highest speed range forward drive is established bymaintaining engagement of brake 68 and clutch 26, releasing clutch 28and engaging brake 29. Power thus remains applied to drive carrier 52 inthe forward direction at input speed but now with sun gear 50 preventedfrom rotation by brake 29, the ring gear 51 and connected transmissionoutput shaft 66 are driven in the forward direction at a speed higherthan converter output speed. The brake 68 may remain engaged on thisupshift since the one-way brake 69 permits the forward rotation of sungear 56 that occurs in this drive. It will also be appreciated thatengine braking is made available in this drive.

Reverse drive is obtained by engaging clutch 28 and brake 86. Withcarrier 52 of front gear set 12 thus held and sun gear 50 driven in theforward direction through clutch 28, the ring gear 51 and connectedoutput shaft 66 are driven in the reverse direction at reduced speed.TRANSMISSION CON- TROL SYSTEM The present invention is embodied in thetransmission control system shown in FIGS. 1 and 2 which system isadapted to control transmission drive arrangements of the type shown inFIG. 1. Generally, the transmission control system is operable toestablish the transmission in five different conditions comprisingneutral, three forward drive ranges and reverse drive. Pump The fluidsuch as oil used in the control system is returned to a sump via variousexhausts in the systems components, the sump being located on theunderside of the transmission housing 15. Fluid pressure for the controlsystem is supplied by a positive displacement pump 91 of conventionaltype which is adapted to be driven by the converters pump 16 and is thusdriven when the vehicle's engine is running. The engine driven pump 91draws fluid from sump 90 through an intake line 92 and delivers it underpressure to a main line 94. Main line 94 is always connected to deliverfluid to a main line pressure regulator valve 96, a modulator valve 97,a governor valve 98, a 1-2 shift valve 99, a transition valve 100, and amanual valve 101. Manual Valve The manual valve 101 determines theoperation of the control system and thus that of the transmission drivearrangement and comprises a spool valve element 102 having spaced landsa and b of equal diameter located in a valve body bore 104. The valveelement 102 is movable to five positions which are Reverse (R), Neutral(N), Drive range (D), Intermediate range (1), and Low range (L). Thevalve element 102 is adapted at its left end 107 to be operated throughsuitable conventional linkage by the operator of the vehicle whomanually selects the position.

When the valve element 102 is in the D position as shown, main line 94is connected between lands a and b to a drive range line 108 while thevalve bore 104 to the left of land a and to the right of land b isexhausted through the valve bores open ends to the sump 90. The driverange line 108 is connected to chamber-72 of brake 68. When valveelement 102 is moved to the I position, main line 94 remains connectedto drive range line 108 and is in addition connected between lands a andb to an intermediate range line 109. When valve element 102 is moved tothe L position, the main line 94 remains connected between lands a and bto both the drive range line 108 and the intermediate range line 109 andis in addition connected between these lands to a low range line 111.When valve element 102 is moved to the N position, the main line 94 isblocked at the manual valve between lands a and b. When the valveelement 102 is moved to the R position, the main line 94 is connectedbetween lands a and b to a reverse line 112 which is connected to servo87 that operates brake 86.

Governor Valve The governor valve 98 which receives fluid from the mainline 94 is of a conventional type. Governor valve 98 is adapted to bedriven by the transmission output shaft 66 and operates to provide in agovernor line 114 a governor pressure which increases with increasingtransmission output speed and thus vehicle speed. The governor valve 98may, for example, be of the type disclosed in U.S. Pat. No. 2,762,384issued to M. S. Rosenberger. For a more detailed description of theoperation of the governor valve, reference may be made to theaforementioned Rosenberger patent. Modulator Valve The modulator valve97 which receives fluid from the main line 94 is of a conventional typethat is controlled by engine manifold pressure. Modulator valve 97operates to provide in a modulator line 115 a modulator pressure whichincreases with increasing engine torque. The modulator valve 97 may, forexample, be of the type disclosed in U.S. Pat. No. 3,509,784 issued toJ. E. Mahoney. For a more detailed description of the operation of themodulator valve, reference may be made to the aforementioned Mahoneypatent. Pressure Regulator Valve The pressure regulator valve 96 is of aconventional type and operates to regulate the pressure in main line 94and also deliver fluid via a line 116 to supply converter 10. Fluid isdelivered from converter to a line 117 which directs the fluid through acooler 118 and then to lubricate various components of the transmissionprior to return to sump 90. The pressure regulator valve 96 is connectedto receive modulator pressure from modulator line 115 and is alsoconnected to receive main line pressure from the reverse line 112 whenpressure in the latter line becomes available. Pressure regulator valve96 operates with these signals to increase the regulated pressure inmain line 94 with increasing engine torque in all of the forward drivesand also to boost the regulated main line pressure in reverse drive. Thepressure regulator valve 96 may, for example, be of the type disclosedin the aforementioned Mahoney patent to which reference may be made fora more detailed description. 1-2 Shift Valve The 1-2 shift valve 99provides for shifting between the first and second forward drives andcomprises a spool valve element 120 having spaced lands a, b and c ofequal diameter located in a valve body bore 121. A cylindrical plug 124is located in the left end of bore 121 which is closed at both ends.This arrangement provides a chamber 125 at the left end of plug 124, achamber 126 between plug 124 and valve element 120 and a chamber 127 atthe right end of valve element 120. Chambers 125, 126 and 127 areconnected to the modulator line 115, low range line 111 and governorline 114, respectively. A spring 128 located in chamber 126 urges plug124 and valve element 120 apart and normally yieldingly holds valveelement 120 in a downshift position as shown. in the downshift position,the main line 94 is connected between lands a and b to a 2-3 line 129while a line 130 connected to chamber 46 of clutch 26 is connectedbetween lands b and c to an exhaust port 131 and an exhaust line 134whose purpose is described in more detail later is blocked by land a.Governor pressure in chamber 127 acts leftward on valve element 120 toprovide an upshift bias opposing the downshift bias provided by spring128 and the modulator pressure in chamber 125 acting rightward on plug124. When the upshift bias is sufficient to overcome the downshift bias,valve element 120 moves leftward to an upshift position. In the upshiftposition, the exhaust port 131 is blocked by land 0, main line 94 isconnected between lands b and c to line 130 and the exhaust line 134 isconnected between lands a and b to the 2-3 line 129. 2-3 Shift Valve A2-3 shift valve 136 provides for shifting between the second and thirdforward drives and comprises a spool valve element 138 having spacedlands a, b and c of equal diameter located in a valve body bore 139. Acylindrical plug 141 is located in the left end of bore 139 which isclosed at both ends. This arrangement provides a chamber 142 at the leftend of plug 141, a chamber 144 between plug 141 and valve element 138and a chamber 146 at the right end of valve element 138. The chambers142, 144 and 146 are connected to the modulator line 115, intermediaterange line 109 and governor line 114, respectively. A spring 148 locatedin chamber 144 urges plug 141 and valve element 138 apart and normallyyieldingly holds valve element 138 in a downshift position as shown. Inthe downshift position, the 2-3 line 129 is connected between lands aand b to a 3-4 line 150 and the intermediate range line 109 is connectedbetween lands b and c to a line 151 that is connected to chamber 82 ofbrake 78 while lands a and b block drive range line 108 and an exhaustport 154, respectively. When the upshift bias provided by governorpressure in chamber 146 acting leftward on valve element 138 issufficient to overcome the downshift bias provided by spring 148 andmodulator pressure in chamber 142 acting rightward on plug 141, valveelement 138 is moved leftward to an upshift pbsition; ln the upshiftposition the drive range line 108 is connected between lands a and b tothe 3-4 line 150, the line 151 is connected between lands b and c toexhaust port 154, and the intermediate range line 109 is blocked by landc. 34 Shift Valve A 34 shift valve 156 provides for shifting between thethird and fourth forward drives and comprises a cylindrical plug 158 anda spool valve element 159 having spaced lands a, b and c of equaldiameter located in a valve body bore 160. The right end of bore 160 isclosed to provide a chamber 163 which is connected to governor line 114and the left end of the valve bore is closed to provide a chamber 165that is connected to modulator line 115. A chamber 167 between plug 158and valve element 159 is connected to an exhaust port 168. A spring 169located in chamber 167 urges plug 158 and valve element 159 apart andnormally yieldingly holds valve element 159 in a downshift position asshown. In the downshift position an exhaust port 171 is blocked by landa, the 34 line 150 is connected between lands a and b to a line 172 thatis connected to chamber 35 of clutch 28 and a line 174 which isconnected to chamber 39 of brake 29 is connected between lands b and cto an exhaust port 176. When the upshift bias provided by governorpressure in chamber 163 acting leftward on valve element 159 overcomesthe downshift bias provided by spring 169 and modulator pressure inchamber 165 acting rightward on plug 158, the valve element 159 is movedleftward to an upshift position in which the line 172 is connectedbetween lands a and b to exhaust port 171, the 3-4 line 150 is connectedbetween lands b and c to line 174, and exhaust port 176 is blocked byland 0.

Sequential shifting by the shift valves 99, 136 and 156 is effected bytheir respective springs having a relatively low, intermediate and highpreload. Thus, the shift valves 99, 136 and 156 will shift at relativelylow, intermediate and high governor pressures and thus vehicle speeds,respectively, assuming the modulator bias remains constant 1-2Transition Valve The 1-2 transition valve controls the transition fromfirst to second forward drive and comprises a spool valve element 180having spaced lands a and b of equal diameter located in a valve bodybore 181. The bore 181 to the right of land b is exhausted by an exhaustport 184 and accommodates a spring 186 which urges the valve element 180to the position shown which will be called a shift-prevent position forreasons which will become more apparent later. In the shift-preventposition, the exhaust line 134 from the 1-2 shift valve 99 is blockedfrom an exhaust port 188 by land b. The left end of bore 181 is closedto provide a chamber 189. The main line 94 is connected through a flowrestriction 191 to chamber 189 and is also connected as best shown inFIG. 2 by a threaded fitting 193 to a passage 194 drilled in bulkhead 36of the transmission housing 15. Thus, drilled passage 194 is anextension of main line 94 downstream of flow restriction 191. Thepassage 194 extends radially inward, then turns and extends axiallyrearward toward the front gear set 12 and has an end 196 in a face 197of bulkhead 36 that faces sun gear 50 of front gear set 12. Aring-shaped valve member 198 is located for limited axial movementbetween bulkhead face 197 and the left side of sun gear 50 and incooperation with the passage end 196 provides an exhaust valve whoseopening and closing is controlled by sun gear 50. When sun gear 50 isthrust rightward, fluid pressure in passage 194 transmitted through thispassages end 196 urges valve member 198 rightward with the sun gear 50to an open position to exhaust passage 194 of fluid pressure and thusprevent pressure buildup in chamber 189 so that the 1-2 transition valve100 remains conditioned in its shift-prevent position by itsspring bias.During such pressure relief of chamber 189, the flow restriction 191maintains the normal main line pressure upstream of this flowrestriction. Alternatively, when the sun gear 50 is thrust leftward, thevalve member 198 is moved by this gearing member to close passage end196 so that pressure in chamber 189 of the 1-2 transition valve 100 thenincreases to full main line pressure to urge valve element 180 rightwardagainst the spring bias to a shift-permit position in which the exhaustline 134 from the 1-2 shift valve 99 is connected between lands a and bto exhaust port 188.

7 CONTROL 8mm OPERATION The control system described above is operableto provide manual selection of reverse, drive and neutral and is alsooperable to provide manual selection of automatic shifting between allforward drives and just between the first and second forward drives andalso provides for holding the first forward drive.

Neutral Position For initiating vehicle operation, the operationconditions the manual valve 101 in its N position and then on startingthe vehicles engine, the pump 91 delivers fluid via main line 94 to thepressure regulator valve 96, modulator valve 97, governor valve98, 1-2shift valve 99 and 1-2 transition valve 100. The pressure regulatorvalve 96 regulates the pressure in main line 94 at the desired value andalso delivers fluid to the converter 10 for its operation. Modulatorpressure is zero with the engine idling and the governor pressure isalso zero with the vehicle stationary. The manual valve 101 blocks themain line 94 from all the lines leading from this valve and with all ofthe shift valves downshifted, the main line 94 is connected in cascadefashion through the shift valves via the 2-3 line 129 and 3-4 line 150to line 172 which delivers the fluid to engage clutch 28 to thus readythe transmission for operation in either forward or reverse direction.

Reverse Drive Position When the operator moves the manual valve 101 toits R position, the main line 94 is then connected to supply fluid tothe reverse line 1 12 which delivers the fluid under pressure to servo87 to engage brake 86. Reverse line 112 also transmits main linepressure to the pressure regulator valve 96 where it acts to boost theregulated main line pressure. The clutch 28 has remained engaged on theshift from neutral since all of the shift valves remain downshifted andthus the reverse drive is established to drive the vehicle.

Drive Range Position When the operator, moves the manual valve 101 toits D position, the main line 94 is then connected to supply the driverange line 108 which delivers the fluid'under pressure to engage brake68. The clutch 28 has remained engaged on the shift from neutral becauseall of the shift valves remain downshifted and thus the first forwarddrive is established to drive the vehicle forwardly.

With the first forward drive thus established and when the engine isaccelerated to propel the vehicle, governor pressure is then produced ingovernor line 114 to urge upshift of all of the shift valves. Inaddition, modulator pressure is being developed in modulator line 115 bythe modulator valve 97 to add to the spring biases in resistingupshifting of the shift valves. When the upshift bias is effective toovercome the downshift bias on the 1-2 shift valve 99, this valve ismoved to its upshift position where it connects the 'main line 94 to theline 130 so that the latter line then delivers fluid under pressure toengage clutch 26. The 2-3 line 129 and thus the 3-4 line 150 and line172 are connected to the exhaust line 134 recognizing that the 2-3 shiftvalve 136 and 3-4 shift valve 156 remain downshifted. For the purpose ofgenerally describing the automatic shifting sequence, it willbe assumedthat the 1-2 transition valve 100 is in its shift-permit position sothat the exhaust line 134 is thus connected to exhaust port 188 topermit release of the clutch 28 so that the first forward drive isreleased and the second forward drive is thus established.

With the l2 shift valve 99 in its upshift position and on continuousacceleration of the vehicle, the upshift bias on the 23 shift valve 136will eventually overcome the downshift bias acting thereon to urge the2-3 shift valve to its upshift position. In the upshift condition, thedrive range line 108 is again connected to the 3-4 line 150 and thus tothe line 172 to reengage clutch 28 since the 3-4 shift valve 156 remainsdownshifted.

With both the l-2 and 2-3 shift valves in their upshift positionestablishing the third forward drive and then when the vehicle speedincreases to a speed such that the upshift bias acting on the 3-4 shiftvalve 156 overcomes the downshift bias acting thereon, the 3-4 shiftvalve upshifts to connect the line 172 to exhaust port 171 to releaseclutch 28 while connecting the 3-4 line 150 to line 174 to engage brake29 to establish the fourth forward drive, the line 172 being fed fromthe drive range line 108 via the upshifted 2-3 shift valve 136.

Sequential downshifting through all of the forward drives occurs whenthe governor pressure upshift biases decrease sufficiently to permit themodulator and spring downshift biases to effect reversal of theoperation described above.

1 Position When the manual valve 101 is moved to its l position, thedrive range line 108 remains connected to main line 94 and in additionthe intermediate range line 109 is connected to main line 94. Fluid inintermediate range line 109 is delivered to chamber 144 of the 2-3 shiftvalve 136 to hold this valve in its downshift position. In addition, theintermediate range line 109 is connected by the 2-3 shift valve 136 tothe line 151 to engage brake 78. Thus, the l-2 shift valve remainsoperable to provide shifting between the first and second forward drivesas described previously but upshifts to the third and fourth forwarddrives are prevented since the 2-3 shift valve 136 is prevented fromupshifting. in addition, engine braking is then possible in the firstand second forward drives since brake 78 is now engaged.

Low Range Position I When the manual valve 101 is moved to its Lposition, both the drive range line 108 and the intermediate range line109 remain connected to the main line 94 and in addition the low rangeline 111 is connected to the main line. The low range line then deliversfluid at main line pressure to chamber 126 of the 1-2 shift valve 99 tohold this valve in its downshift position. Thus, the transmission isheld in low drive since neither the 2-3 shift valve l36 nor the 3-4shift valve 156 can upshift. Furthermore, engine braking is possible inthis low drive since engagement of brake 78 is maintained by thedownshifted 2-3 shift valve 136.

1-2 Transition Valve Operation It will be recalled that in the abovedescription of operation regarding release of the first forward drive,it was assumed that the 1-2 transition valve was in its shift-permitposition. Describing now the complete operation of this valve, wheneverfirst forward drive is established with clutch 28 engaged by supply offluid via all of the shift valves in their downshift positions andclutch 26 disengaged by the 1-2 shift valve 99, the thrustreaction ofthe sun gear 50 is rearward or to the right; This permits the fluidpressure in passage 194 to move valve member 198 rightward so thatpressure is prevented from building in chamber 189 of the transitionvalve 100. With no pressure buildup in chamber 189, the spring 186yieldingly holds the valve element 180 in its shiftprevent positionblocking the l-2 shift valves exhaust line 134 from the exhaust port188. Then, on a shift demand from the first to the second forward drive,which is accomplished by the l-2 shift valve 99 moving to its upshiftposition, the main line 94 is opened to the line to initiate engagementof clutch 26 while the line 172 is connected by the shift valves 156 and136 and then 1-2 shift valve 99 to exhaust line 134. When chamber 46 ofclutch 26 is filled and pressure starts to rise to engage this clutch,the engagement of clutch 28 is held up or maintained since the chamber35 of clutch 28 is prevented from being exhausted by the l-2 transitionvalve 100. When the pressure in chamber 46 of clutch 26 is sufficientlyhigh enough to provide clutch 26 and thus the second forward drive withsufficient torque capacity to drive the load, the drive from theconverter to the gearing switches from sun gear 50 in front gear set 12to ring gear 58 in rear gear set 14. This reverses the thrust reactionon sun gear 50 causing it to move leftward and thus move the ring member198 to close the passage end 196. .With passage 194 thus closed, exhaustof fluid from chamber 189 of the l-2 transition valve 100 is prevented.This causes the pressure in chamber 189 to immediately rise to full mainline pressure which pressure acting in chamber 189 is effective to biasthe 1-2 transition valve 100 to its shift-permit position in which itconnects the exhaust line 134 to the exhaust port 188 to thus releasethe clutch 28.

Thus, on shifting from the first to the second forward drive, the 1-2transition valve 100 maintains the first forward drive engaged to drivethe load until the second forward drive is established with sufficienttorque capacity to drive the load. This positively prevents driveinterruption on such shifting and also provides a smooth feeling shift.

The above-described embodiment is illustrative of the invention whichmay be modified within the scope of the appended claims.

I claim:

1. In a control system for a transmission the combination oftransmission means including gearing and a plurality of fluid pressureoperated drive establishing means for providing a plurality of differenttransmission drives to drive a load on selective delivery of fluidpressure to said fluid pressure operated drive establishing means, asource of fluid pressure, shift valve means for determining selectivedelivery of fluid from said source to said fluid pressure operated driveestablishing means to effect establishment of and shifting between saidtransmission drives, said gearing including a member that undergoes aload reversal when one of said transmission drives is released andanother of said transmission drives is established to transmit torque todrive the load, and transition valve means controlled by said gearingmember on shifting from said one transmission drive to said anothertransmission drive for maintaining fluid pressure in the fluid pressureoperated drive establishing means establishing said one transmissiondrive to maintain said one transmission drive until said anothertransmission drive is established with sufficient torque capacity todrive the load.

2. In a control system for a transmission the combination oftransmission means including gearing and a plurality of fluid pressureoperated drive establishing means for providing a plurality of differenttransmission drives to drive a load on selective delivery of fluidpressure to said fluid pressure operated drive establishing means, asource of fluid pressure, shift valve means operable in one condition toprovide for delivery of fluid from said source to one of said fluidpressure operated drive establishing means to establish one of saidtransmission drives and operable in another condition to provide fordelivery of fluid from said source to another of said fluid pressureoperated drive establishing means to establish another of saidtransmission drives while providing for exhaust of fluid from said onefluid pressure operated drive establishing means to release said onetransmission drive, transition valve means operable in one condition toprevent exhaust of fluid from said one fluid pressure operated driveestablishing means when said shift valve means is in its said othercondition to effect maintenance of said one transmission drive whilesaid shift valve means is in its said other condition providing forestablishment of said other transmission drive, said transition valvemeans operable in another condition to exhaust said one fluid pressureoperated drive establishing means when said shift valve means is in itssaid other condition to effect release of said one transmission drivewhen said another transmission drive is established, means normallyyieldingly holding said transition valve means in its said onecondition, said gearing including a member that undergoes a loadreversal on shifting from said one transmission drive to said othertransmission drive, and bias means controlled by said gearing member forbiasing said transition valve means to its said other condition topermit release of said one transmission drive only when said othertransmission drive is established with sufficient torque capacity todrive the load.

3. ln a control system for a transmission the combination oftransmission means including gearing and a plurality of fluid pressureoperated drive establishing means for providing a plurality of differenttransmission drives to drive a load on selective delivery of fluidpressure to said fluid pressure operated drive establishing means, asource of fluid pressure, shift valve means operable in one condition toprovide for delivery of fluid from said source to one of said fluidpressure operated drive establishing means to establish one of saidtransmission drives and operable in another condition to provide fordelivery of fluid from said source to another of said fluid pressureoperated drive establishing means to establish another of saidtransmission drives while providing for exhaust of fluid from said onefluid pressure operated drive establishing means to release said onetransmission drive, transition valve means operable in one condition toprevent exhaust of fluid from said one fluid pressure operated driveestablishing means via said shift valve means when said shift valvemeans is in its said other condition to effect maintenance of said onetransmission drive while said shift valve means is in its said othercondition providing for establishment of said other transmission drive,said transition valve means operable in another condition to exhaustsaid one fluid pressure operated drive establishing means via' saidshift valve means when said shift valve means is in its said othercondition to effect release of said one transmission drive when saidanother transmission drive is established, means normally yieldinglyholding said transition valve means in its said one condition, fluidchamber means connected through a fluid restriction to receive fluidfrom said source for effecting a fluid pressure bias to urge saidtransition valve means to its said other condition, exhaust passagemeans connected to said fluid chamber means, and said gearing includinga member that undergoes a load reversal on shifting from said onetransmission drive to said other transmission drive and is operable whensaid one transmission drive is driving the load to provide for openingsaid exhaust passage means to exhaust said fluid chamber means to permitmaintenance of said transition valve means in its said one condition bysaid biasing means and is further operable on establishment of saidother transmission drive with suflicient torque capacity to drive theload to then close said exhaust passage means to permit pressure buildupin said fluid chamber means so that said transition valve means ispressure biased to its said other condition to only then permit releaseof said one transmission drive whereby said one transmission drive ismaintained until said other transmission drive is established withsufficient torque capacity to drive the load.

1. In a control system for a transmission the combination oftransmission means including gearing and a plurality of fluid pressureoperated drive establishing means fOr providing a plurality of differenttransmission drives to drive a load on selective delivery of fluidpressure to said fluid pressure operated drive establishing means, asource of fluid pressure, shift valve means for determining selectivedelivery of fluid from said source to said fluid pressure operated driveestablishing means to effect establishment of and shifting between saidtransmission drives, said gearing including a member that undergoes aload reversal when one of said transmission drives is released andanother of said transmission drives is established to transmit torque todrive the load, and transition valve means controlled by said gearingmember on shifting from said one transmission drive to said anothertransmission drive for maintaining fluid pressure in the fluid pressureoperated drive establishing means establishing said one transmissiondrive to maintain said one transmission drive until said anothertransmission drive is established with sufficient torque capacity todrive the load.
 2. In a control system for a transmission thecombination of transmission means including gearing and a plurality offluid pressure operated drive establishing means for providing aplurality of different transmission drives to drive a load on selectivedelivery of fluid pressure to said fluid pressure operated driveestablishing means, a source of fluid pressure, shift valve meansoperable in one condition to provide for delivery of fluid from saidsource to one of said fluid pressure operated drive establishing meansto establish one of said transmission drives and operable in anothercondition to provide for delivery of fluid from said source to anotherof said fluid pressure operated drive establishing means to establishanother of said transmission drives while providing for exhaust of fluidfrom said one fluid pressure operated drive establishing means torelease said one transmission drive, transition valve means operable inone condition to prevent exhaust of fluid from said one fluid pressureoperated drive establishing means when said shift valve means is in itssaid other condition to effect maintenance of said one transmissiondrive while said shift valve means is in its said other conditionproviding for establishment of said other transmission drive, saidtransition valve means operable in another condition to exhaust said onefluid pressure operated drive establishing means when said shift valvemeans is in its said other condition to effect release of said onetransmission drive when said another transmission drive is established,means normally yieldingly holding said transition valve means in itssaid one condition, said gearing including a member that undergoes aload reversal on shifting from said one transmission drive to said othertransmission drive, and bias means controlled by said gearing member forbiasing said transition valve means to its said other condition topermit release of said one transmission drive only when said othertransmission drive is established with sufficient torque capacity todrive the load.
 3. In a control system for a transmission thecombination of transmission means including gearing and a plurality offluid pressure operated drive establishing means for providing aplurality of different transmission drives to drive a load on selectivedelivery of fluid pressure to said fluid pressure operated driveestablishing means, a source of fluid pressure, shift valve meansoperable in one condition to provide for delivery of fluid from saidsource to one of said fluid pressure operated drive establishing meansto establish one of said transmission drives and operable in anothercondition to provide for delivery of fluid from said source to anotherof said fluid pressure operated drive establishing means to establishanother of said transmission drives while providing for exhaust of fluidfrom said one fluid pressure operated drive establishing means torelease said one transmission drive, transition valve means oPerable inone condition to prevent exhaust of fluid from said one fluid pressureoperated drive establishing means via said shift valve means when saidshift valve means is in its said other condition to effect maintenanceof said one transmission drive while said shift valve means is in itssaid other condition providing for establishment of said othertransmission drive, said transition valve means operable in anothercondition to exhaust said one fluid pressure operated drive establishingmeans via said shift valve means when said shift valve means is in itssaid other condition to effect release of said one transmission drivewhen said another transmission drive is established, means normallyyieldingly holding said transition valve means in its said onecondition, fluid chamber means connected through a fluid restriction toreceive fluid from said source for effecting a fluid pressure bias tourge said transition valve means to its said other condition, exhaustpassage means connected to said fluid chamber means, and said gearingincluding a member that undergoes a load reversal on shifting from saidone transmission drive to said other transmission drive and is operablewhen said one transmission drive is driving the load to provide foropening said exhaust passage means to exhaust said fluid chamber meansto permit maintenance of said transition valve means in its said onecondition by said biasing means and is further operable on establishmentof said other transmission drive with sufficient torque capacity todrive the load to then close said exhaust passage means to permitpressure buildup in said fluid chamber means so that said transitionvalve means is pressure biased to its said other condition to only thenpermit release of said one transmission drive whereby said onetransmission drive is maintained until said other transmission drive isestablished with sufficient torque capacity to drive the load.